I can't imagine what an "essay writing service provider" is, but getting someone else to do the work for you won't make you better at it.
The best way to become a good essayist is to gain a full understanding of your subject, and express your points in intelligent ways. A thesaurus can be invaluable. Make a couple of rough drafts before the final version. Proofread. If you can write a simple story, an essay is another step beyond that.